The invention relates to the field of manufacturing a control disc or a control plate for a liquid-ring machine and, more particularly, to the economical manufacture of such a control disc or plate for withstanding corrosive media.
Electric machines known in the art as liquid ring machines generally are employed as pumps for a gaseous medium. A housing for such a pump surrounds a ring of rotating liquid which is caused to rotate by an eccentrically mounted vane wheel turned by a revolving shaft. The shaft, in turn, is supported at each end in an end bell having inlet and outlet ports for the gaseous medium to be pumped as well as at least one inlet for operating liquid which replenishes any liquid lost, for example, through evaporation into the pumped medium. Because of the eccentric mounting of the vane wheel, operating liquid on one side Of the vane wheel creates a suction zone in which zone the pumped gaseous medium is sucked into the pump by way of the inlet ports in the end bells. On the other side of the eccentrically mounted vane wheel, a pressure zone is created where the pumped gaseous medium is forced to exit the pump by way of the outlet ports in the end bells.
Between the end bells and the vane wheel housing or comprising a part of the end bell itself is a control disc or plate which partitions the end bell into separate chambers for operating liquid and pumped gaseous medium as well as provides control openings for the entry and exit of both operating liquid and gaseous medium. The control disc is typically sealed with the end bell on one side and seals the housing on the other side. At the same time, the control disc is designed to comprise separate pressure and suction slots in an end face wall facing the liquid ring for the pumped gaseous medium, the pressure and suction slots being concentrically arranged outside a hub of the vane wheel. Also, an opening for operating liquid is typically arranged in the vicinity of the vane wheel hub so that the operating liquid further fulfills the function of a gap sealing liquid sealing the gap between the vane wheel hub and the control disc.
In known methods of manufacture of such control discs, at least one of the two end bells is designed as including a side shield abutment with inlets and outlets for a medium to be transported as Well as with connections for supplying cooling and gap-sealing operating liquid. Also, between the side shield abutment and the housing, a control disc with suction and pressure slots on its end face (facing the liquid ring) as well as at least one passage for the operating liquid through the end face wall is provided, where the various openings in the end face wall Of the control disc facing the liquid ring are further in communication with chambers bounded between the side shield abutment and the control disc by means of partitions on the back of the control disc and/or in the side shield abutment of the end bell.
It is further known from the manufacture of liquid-ring machines such as the Siemens type 2BB to combine the control disc and the side shield abutment to form a structural unit referred to hereinafter as a control plate.
Both control discs and control plates are commonly cast of steel in expensive molds where the end face wall must be relatively thick because of the requirements of casting processes of present foundry technology. In addition, the outside surface of the end face wall facing the vane wheel must be machine planed smooth and the edges of the openings must be deburred and brought to accurate dimensions in order to obtain a uniform gap width between the end face wall and the vane edges of the vane wheel to permit a flow through the openings of the end face wall that is as undisturbed as possible.
With more corrosive media, increased corrosion occurs when ordinary steel is employed for constructing the end face wall at the openings. Such corrosion leads to a premature, noticeable degradation of the efficiency of such machines because of increased gap losses and disturbed flow conditions through the openings in the end face wall.
For such aggressive media, control discs made of substantially more expensive corrosion resistant steel alloys are known, either manufactured by a casting process or by burning-out the spaces and openings from a correspondingly thick-walled alloy steel plate, the latter method resulting in a considerable loss of expensive material.
In cast control plates for withstanding a corrosive medium of the Siemens type 2BB, a relatively thin-walled alloy steel cover disc with preformed openings is typically screwed on to an end face wall of a pre-cast steel side shield abutment after a chip-removing machining of the outside surface of the end face wall and preforming a circular edge in the cover disc. Also, the space between the outer circumference of the end face wall and the circular edge of the cover disc is typically cast with hardenable casting resin so that no corrosive medium can get between the cover disc and the cast end face wall.
With this Siemens control shield, the edges of the aligned openings in the end face wall and in the cover disc must be reworked together in a final operation.
Thus, it is desirable to provide a method of manufacture of a control disc or a control plate for a liquid-ring machine for withstanding more corrosive media which results in a lower cost for material and a greater simplicity of manufacture and obtains practically the same service life for the control disc or plate obtained with the designs cast wholly of corrosion resistant steel alloy, or designs made using a burn out process.